In astrophysics the term "metals" refers to all the elements heavier than helium, in contrast to the terminology adopted in other scientific disciplines, in part because all these elements make up a small contribution in number and mass with respect to H and He.
A considerable fraction of the metals (and most of the iron) do not reside in the galaxies of groups and clusters and they have been expelled in their surrounding X-ray emitting hot atmospheres (for the purpose of this review we will define the hot atmosphere of groups as intra-group medium, IGrM). Indeed the iron share, i.e. the ratio of iron in the hot atmosphere and the iron locked up in stars in the galaxies, ranges from 1 up to 10 [1]}, [2]}. Therefore the key question is to understand the main transport mechanisms responsible for that unbalance [3]}, [4]}. There are two broad categories of mechanisms: i) extraction by ram pressure stripping and galaxy-galaxy interactions; ii) ejection by galactic winds powered from inside the galaxies themselves either by SNe (stellar feedback) or by the supermassive black hole (SMBH) at their center (in the so-called active galactic nucleus, AGN, feedback). Other important processes redistributing the metals within the hot atmospheres are the central AGN uplift of metals [5]}, [6]}, [7]}, [8]} and sloshing, i.e. the offset of the bulk of central part of the hot atmosphere from its hydrostatic equilibrium in its gravitational potential and the subsequent oscillations that may broaden the original distribution at larger scales [9]}, [10]}. Another source of metals could be the diffuse stellar component not associated to any single galaxy but to the global halo of the cluster or group (also know as intra-cluster light, ICL) polluting the ICM and the IGrM in situ [11]}.
